The present invention generally relates to the design and manufacture of spaceframe structures, and more particularly relates to the design and manufacture of upper stage intertank structures for space vehicles.
Prior art designs for certain structural components of space vehicles, such as the upper stage intertank structure of the Boeing Delta III and Delta IV launch vehicles, have been configured with X-shaped structural elements, referred to hereinafter as X-panels. One such X-panel 100 is shown in FIG. 1. This type of X-panel has been fabricated from either aluminum or a composite material, but studies have indicated that a composite material design allows meeting structural performance requirements with less weight and lower costs, in comparison to aluminum.
An existing X-panel 100 generally incorporates two full-length adhesively bonded joints between two molded panel halves, plus numerous mechanical fasteners 102. As such, the X-panel design is labor-intensive, and relatively costly to manufacture. Moreover, the load path eccentricity 101 at the intersection of the two legs of the xe2x80x9cXxe2x80x9d (X-panel members 103, 104) typically requires local reinforcement with an associated weight penalty. In addition, the cross-section of the X-panel design, as shown in FIG. 2, frequently includes a central web 105, which also adds unwanted weight to the structure.
Accordingly, it is desirable to modify the design and fabrication of the aforementioned X-shaped structural element (X-panel 100) to reduce the associated labor and manufacturing costs, and to increase the structural efficiency of the intersection joint 101. In addition, it is desirable to modify the design of the X-panel 100 to reduce its weight contribution to the upper stage intertank, or any other structural component, of a space vehicle assembly. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
An apparatus is provided for a tubular composite structure, which requires no adhesively bonded or mechanically fastened joints. The apparatus comprises intersecting tubular struts, each strut having a top face connected to a bottom face by side walls. The tows (bundles of reinforcing fibers) comprising the intersecting side walls of the struts are interwoven with each other to form a seamless integral joint between the struts. This technique can be used to form intersecting composite tubes of any cross sectional shape, and is not restricted to the rectangular cross sections shown in the accompanying drawings.
A method is provided for fabricating the tubular composite structure. The method comprises the following steps:
a) layering parallel strands of a composite material in an alternately crossing orientation to form intersecting bottom faces of the tubular composite structure;
b) building up from the intersecting bottom faces, strand layers of the composite material in an alternately crossing orientation to form intersecting side walls of the tubular composite structure;
c) layering parallel strands of the composite material in an alternately crossing orientation to form intersecting top faces of the tubular composite structure, the intersecting top faces corresponding to the configuration of the intersecting bottom faces and the intersecting side walls;
d) oven curing the composite material, using a combination of external and internal tooling to control the tube configuration during cross-linking of the composite matrix material;
wherein the layers of parallel strands forming intersecting bottom and intersecting top faces, and the layers of strands forming intersecting side walls, run continuously through the tubular composite structure to form a seamless integral intersection joint.